1. Field of the Invention
This invention relates to magnetic thin films for use in electronic recording heads and to a method for preparing such films. More particularly, this invention relates to such thin films as are comprised of electromagnetic films of preferably, NiFe and designed to reduce the number of domains and Barkhausen noise levels in the recording heads in which such films are used.
2. Description of the Prior Art
The trends toward higher density magnetic storage devices in electronic data processing equipment require the use of smaller dimensions for the inductive read/write or magnetic recording heads used in such equipment. However, as the width of the pole tip in such heads becomes very narrow, that is, narrower than about 2 times the domain wall width, and the thickness of the magnetic film is not increased, the shape of the recording head begins to dominate the structure of the magnetic domain (J.P. Lazzari and I. Melnick, IEEE-Transactions On Magnetics, MAG-7, 146, 1971). The resulting structure can then impair the performance of the recording head by introducing Barkhausen noise and by decreasing the signal to noise ratio.
Lamination of the magnetic heads has been proposed as a means to control domain structure on recording heads of these dimensions (J. S. Y. Feng and D. A. Thompson, IEEE Transactions On Magnetics, MAG-13, 1521, 1977).
It has been postulated by the present inventors that in such structures the laminating layers should also be non-magnetic, continuous and pore free with thicknesses between 10 and 400 angstroms (.ANG.), in order to provide optimum benefits in terms of reducing the level of Barkhausen noise and increasing the signal to noise ratio.
Furthermore, to be practically useful the non-magnetic laminating layers should obviously retain their properties during the thermal cycling which is employed during the manufacturing and/or use of the composite laminates.
The use of a quenching type non-magnetic lamination material would further insure the integrity of the composite film and tend to relax. The pore-free requirements of the non-magnetic layer. The non-magnetic property of the lamination material should, advantageously, result from quenching rather than from simple dilution.
J. V. Powers (IBM Technical Disclosure Bulletin, vol. 20, No. 11B, April 1978, "Individualization of Bubble Device Overlay Properties") reported that:
"In the fabrication of bubble devices, the coercivity of permalloy used to move bubble domains is often a function of underlays onto which the permalloy is deposited. NiP is one such underlay. It has been found that the coercivity of permalloy on a NiP underlay will depend on the thickness of the underlay, for thicknesses up to about 800 angstroms, if the following bath is used for plating of the underlayer.
The NiP plating bath is as follows:
______________________________________ NiCl.6 H.sub.2 O 109 gms H.sub.3 BO.sub.3 25 gms Sodium Saccharin 8.0 gms Sodium Lauryl Sulfate 0.2 gms Na.sub.2 HPO.sub.2 20 gms H.sub.2 O in sufficient amount to make 1 liter ______________________________________
The variation of permalloy coercivity H.sub.c versus thickness of the NiP underlayer is shown in the figure. A great degree of control is provided over a wide range of NiP. An example of utility of this technique is in the fabrication of bubble domain transfer switches, where it is sometimes desirable to provide a holding field. In such switches, a lesser thickness of NiP underlayer is provided in order to make the permalloy of higher coercivity in the switch area. This permalloy is then used to provide the holding field."
The figure referred to by J. V. Powers is reproduced as FIG. 1 of the drawings of this application.
The NiFe/NiP laminates produced by J. V. Powers were produced from an electroless bath, and as such would have the following shortcomings for use in magnetic recording heads: they would be porous, rough and non-continuous and not of uniform thickness. The J. V. Powers structures were also two layer laminates, with one layer of NiP and one layer of NiFe, which would provide a plurality of domain walls within his structure. The J. V. Powers structures would thus not be useful in thin film magnetic head structures.
Prior to the present invention, therefore, it has not been readily possible to provide dimensionally stable magnetic thin film laminates which also provide optimum benefits in terms of both limiting the number of domains, reducing Barkhausen noise, and increasing the signal to noise ratio, when used in magnetic recording heads using relatively narrow pole tips.
An object of the present invention is to provide novel magnetic thin film laminates for use in magnetic recording heads.
A further object of the present invention is to provide such laminates as are made from laminae of magnetic alloys such as NiFe, CoFe, CoNi, and non-magnetic alloys and metal materials such as NiP, Cr and CrNi that have magnetic quenching properties.
A still further object of the present invention is to provide magnetic recording heads made with such thin film laminates.
A further object of the present invention is to provide magnetic recording heads having as few domains as possible, and preferably no more than one.
A further object of the present invention is to provide magnetic recording heads having a very low Barkhausen noise.
A further object of the present invention is to provide magnetic recording heads having an increased signal to noise ratio.
A further object of the present invention is to provide magnetic thin films which are specifically useful in magnetic recording heads which have pole tips which are narrower in size than about 2 times the domain wall width.